The work was suffering. He was suffering. At 29, Bradley Cooper knew he had to make a decision. Thankfully, he made the right one.

"If I continued it, I was really going to sabotage my whole life," the American Hustle star, now 38, tells GQ's January issue of why he got sober almost a decade ago.

The actor and PEOPLE's 2012 Sexiest Man Alive had a particularly bad run-in with drugs and alcohol around the time of his breakthrough role in Wedding Crashers – he has spoken before of intentionally smashing his head on concrete at a party and ending up in the hospital.

He was never late to the set, but "of course it hindered the work," he says now of that kind of behavior. And once he gave it all up, he experienced something of a personal renaissance.

"I was doing these movies, and I got to meet Sandra Bullock [his costar in 2009's All About Steve] and meet these people and work with them," he says. "And I'm sober, and I'm like, 'Oh, I'm actually myself. And I don't have to put on this air to be somebody else, and this person still wants to work with me? Oh, what the f––– is that about?' I was rediscovering myself in this workplace, and it was wonderful."

Some of his roles weren't creatively fulfilling, he adds, but he felt lucky anyway. "I was grateful and happy to be working," he says, "and filling that void in smaller moments."

Others could see the change, too. And today, his American Hustle costar Amy Adams says there's a sensitive man underneath the guy whom many have always considered a party guy.

"I've just never seen him as a frat boy," Adams says. "I understand how people could perceive that. But he's a very soulful person, a very open person. I think that people can mistake a sort of laid-back quality for that frat thing."